Magnetic core



J. C. GRANFIELD MAGNETIC CORE Filed Jan. 28, 1941 Inventor":

John C; Granfield,

Patented May 2, 1944 MAGNETIC CORE John 0. Graniield, runners, Mass., assignor to General Electric Company, a corporation of New York Application January 28, 1941, Serial No. 376,304 11 Claims. (Cl. 115-356) This invention relates to improvements in laminated magnetic core structures for electrical induction apparatus such as transformers and reactors, and to methods for making such improved core structures.

In the usual construction for magnetic cores,

the laminations are cut or punched from relatively large stock sheets which are produced by a rolling process from bars or billets of a suitable magnetic material such as silicon steel or a magnetic nickel iron alloy. The rolling process produces a grain structure in the sheets which may extendin the direction in which the sheets have been rolled. The path of least magnetic resistance such material is generally in the direction that the sheets have been rolled, though in certain types of steel the most favorable magnetic direction, in so far as low flux losses are concerned, is at some angle with respect to the rolling direction. It has been found that optimum results for magnetic cores are obtained it the laminations are so cut from the sheets of magnetic material that the core flux path is parallel with the path of least magnetic resistance thereof.

One common form oi a magnetic core consists of a stack of L-shaped punchings but it is obvious that such shapes cannot be punched as a single piece from standard stool: in such a manner;. that the most favorable magnetic direction extends parallel with the flux path in both parts 01' the punching. This is due to the fact that the grain extends in the same direction throughout all parts of the stock sheet while the two parts oi an L-shaped punching are at right angles to each other. Another common form of core consists of rectangular laminations stacked at right'angles with respect to each other. While the most favorable magnetic direction in this type oi core may be made parallel with the direction of the flux path throughout the central portion of the laminations, the core flux must cut crosswise of the 7 most favorable direction at the ends of the laminations in traversing from one core leg to the next. Due to this crosswise flow of flux at the corners of the core, relatively high losses occur at these points.

It is therefore a general object of the present invention to provide a new and improved mago More specifically, it is an object of the invention to provide a, new and improved core in which the laminations are so cut from the metal stock that when fitted together into a unit, the core flux may flow in the most favorable magnetic direction of the iaminations substantially completely throughout the magnetic circuit.

Further objects and advantages oi the invention will appear from the following description taken in connection with the accompanying drawing, while the features of novelty will be pointed out with greater particularity in the appended claims.

In the drawing, Fig. 1 is a view in perspective of a magnetic core constructed in accordance with the present invention; Fig. 2 is a view illustrating the method by which the laminations for the core of Fig. 1 may be produced; Fig. 3 is a plan view oi a portion of a magnetic core illustrating a further modification of the invention; Fig. 4 is a view illustrating the manner in which the laminations for the core of Fig. 3 may be produced; Fig, 5 is a plan view of a magnetic core illustrating a still further modification of the invention; and Fig. 6 is a. view illustrating the manner in which the laminations for a core such as shown in Fig. 5 may be produced.

Referring now to Fig. 1 of the drawing, a magnetic core is shown having legs made up of stacks of laminations H and yokes made up of stacks of laminations H. The adjacent stacks are angularly arranged with respect to each other and in the case of the rectangular core as shown, the stacks are arranged at right angles. The ends of the stacks are out at an angle which is less than degrees and substantially equal to one-half of the angle between adjacent stacks whereby the stacks may be fitted together in an end to end relation. In other words, the diagonally cut end of each stack is substantially covered by the similarly or cooperatively cut end of the adjacent stack. It is not essential that the ends oi each laminationv of each stack be out along a straight line or even along similar lines, but it is preferred, however, that, in the case of a rectangular core as shown and having substantially the same cross section in each stack,..the ends of the lines along which the lamination ends are cut terminate on a line which is at 45 degrees with respect to the side edges of the laminations. In any case, the end edges of the adjacent laminations when the core is assembled butt together in a parallel relation to form what will be termed a mitered joint between laminations of each layer and, hence, between the adjacent ends of each pair of angularly arranged stacks.

In order that the reluctance of the magnetic circuit be held to a minimum, the butt joints between the lamination stacks must be made tight, and preferably means be provided for maintaining the tightness of the joints throughout normal usage of the device. Clamping means may be used for holding the leg and yoke portions tightly against each other but such clamps, if solely relied upon for this purpose, would in all probability need to be tightened to such an extent that internal strains might be produced thereby in the laminations which in turn would adversely afi'ect the magnetic properties the metal.

In the modification illustrated in Fig. l',-the ends of the laminations are so shaped and fitted together that a tight joint is assured between the leg and yoke stacks without requiring tight clamping means. The laminations H and I2 are each provided at one end with a dovetail projection ll extending perpendicularly from the diagonal edge and an opening I in the opposite end for cooperatively receiving a similar dovetail projection of the adjacent lamil nation. The projections II and the cooperating openings I are so matched that when the laminations are fitted together in the assembly of the core, there will be no appreciable gap between the ends of adjacent laminations. It will be obvious that after the core has been assembled, subsequent separation oi the legs and yokes of the core will be substantially precluded by virtue of the interlocked portions.

In assembling the lamination layers it is preferred that adjacent layers be oppositely arranged that the projections at the ends of the laminations of adjacent layers will extend in opposite directions. With the layers so arranged, edgewise shifting of the laminations of one layer with respect to each other will be precluded. Only a relatively light clamping means need be provided for holding the lamination layers together and such clamping means need not be drawn so tight as to set up any appreciable strains in the metal of the laminations.

The laminations II and I2 are so cut from the stock sheets of metal that the most favorable magnetic direction oi the metal will run lengthwise of the laminations. When the laminations are assembled as illustrated, due to the mitered joints at the corners of the core, the core flux may flow through the leg and yoke portions substantially continuously in the most favorable magnetic direction of the metal throughout the magnetic circuit and substantially without cutting crosswise of such direction at any point. A highly eilieient magnetic circuit is thus provided.

It is preferred that the laminations be formed from a strip of magnetic material in a manner illustrated in Fig. 2. The strips of magnetic material such as silicon steel or a magnetic nickel iron alloy are preferably produced by the high reduction cold rolled process from bars or billets so that the strips have a granular structure, the grain extending longitudinally of the strips and parallel to their side edges and having the most favorable magnetic direction substantially parallel with the grain direction. The strips may be of any desired width and of indefinite length. The strips are preferably of the exact width of the laminations to be used in the magnetic core.

The laminations may be cut or punched from such a strip I! by any suitable means -(not shown) such as a suitable set of dies. The strip is cut crosswise at recurrent intervals, depending .upon the length or the laminations to be formed, and at an angle substantially equal to one-hali of the angle which is to be formed by two adjacent lamination stack. The direction of the cut across the strip is alternated, or in the case of laminations for a tangular core when each cut will be along a base line at 45 degrees to the strip edge, the alternate cuts will be displaced by degrees from the others. In order that the projection provided on the diagonal end of one lamination will register accurately with the opening thus formed in the end of the next adjacent lamination when placed at right angles with respect thereto, the projection should extend from the exact center of the diagonal and be exactly symmetrical on both sides of a perpendicular erected from the center of the diagona1. It will be obvious that the leg laminations ll may all be punched from one strip and the yoke laminations I! from another, or they may be punched alternately from thesame strip as illustrated in Fig. 2. By either method of punching the laminations, there will be no waste of material.

The particular configuration for the dovetail joints between the leg and yoke laminations is immaterial, it being important only that it be so designed that a minimum amount'of metal extend into the flux path with the grain thereof at an angle other than that of the core flux path.

In producing the cores by this method it is preferred to first punch out the laminations in the manner described and then form desired shapes such as L, U, or rectangular by interlocking component parts and then annealing the assembled shape. :By assembling the shapes first and then annealing them with a proper heat treatment to remove strains produced in the metal by the punching operation,.the interlocked parts will enlarge slightly to further tighten the joint and thereby practically eliminate the gap eflect.

In certain types of cores, it may not be necessary to interlock the laminations in order to insure a suillciently tight joint between the diagonally cut ends. The modifications of core structures illustrated in Figs. 3 to 6, inclusive, are particularly suitable for smaller sized cores, or in cores built up from relatively thin laminations. The magnetic core of Fig. 3 comprises stacks of laminations formin legs III and yokes 2| the laminations for which are so punched from stock sheets of magnetic material that the most favorable magnetic direction thereof extends substantially parallel with the flux path through the laminations, as in the previously described modification. The opposite ends of the leg and yoke laminations are cut diagonally so that the right angularly arranged laminations of each layer fit together at the corners with mitered joints as in the core described above. In this modification, however, the diagonal edge at one end of each of the laminations is provided with a non-interlocking projection 22 while the opposite diagonal edge is provided with a corresponding notch 23 for cooperatively receiving the projection of an adjacent right angularly arranged lamination. As illustrated, the projection and the cooperating notch may be or a semicircular configuration, although it is to be understood that the projection and notch may be of any other suitable shape.

In the assembly of the core of this modification, the laminations of each layer are fitted closely together so that there will be a minimum of space between adjacent ends. The adjacent lamination layers are also oppositely arranged so that the projections of the adjacent lamination layers will extend in opposite directions, as is indicated by the dotted lines in Fig. 3. With the laminations assembled in this manner the projections of each lamination will overlap with portions of right angularly extending laminations of adjacent layers on the opposite sides thereof. The lamination layers may then be compressed by any suitable clamping means (not shown) which are so applied as not to set up any appreciable internal strains within the metal of the laminations which might adversely affect the magnetic properties thereof. 'Due to the frictional resistance between the overlapping portions of the adjacent lamination layers, separation of the leg and yoke portions of the core at the joints will be substantially precluded.

While the laminations for the leg and yoke portions of the core may be cut from stock sheets of magnetic material of any dimension with the most favorable magnetic direction extending parallel to the path of the core flux through the laminations, it is preferred that the laminations be punched from a relatively long narrow strip 25 as shown in Fig. 4. The manner of punching the laminations from the strip is similar to that described above in connection with Fig. 2. In

orderthat the laminations will fit properly together when arranged at right angles with respect to each other, it will be necessary that the diagonal edge be at an angle of 45 degrees with respect to the side edges of the strip and that the projection and the notch provided on the oppo site diagonal edges" of each lamination be symmetrical on the opposite sides of a perpendicular erected from the center of the diagonal. With the endsof the laminations so punched, it will be obvious that the parts may be fitted accurately together with no appreciable gap between the adjacent end edges,

In Fig. is illustrated a further modification of the invention in which a magnetic coreis shown comprising leg portions 30 and yoke portions 3i which are also fitted together with generally diagonally mitered comer joints, or the joints extend from the vicinity of the inner corner to the vicinity of the outer comer of the assembled laminations so that a minimum of fiux passing frontone lamination to another will pass crosswise of the the most favorable magnetic direction, but of a slightly different configuration than those previously described. In this modification one end of each of the laminations is provided with a triangular projection 32 which extends from a true diagonal line while the oppositeend is provided with a corresponding notch 33 for cooperatively receiving a similar projection from a lamination extending at right angles with respect thereto. The base of the triangular projecting portion of each lamination, that is, along the line of the diagonal, is preferably just slightly narrower than the length of the diagonal, while the height of the triangle is of the order of onefourth of the width of the base. Thus, it will be observed that the width of each lamination increases progressively from zero at the outermost end to maximum width at the inner corners of the diagonal edges. The rate of progressive increase of width varies from minimum to maximum along the end edge of the laminations depending upon the particular angles of the two sides of the triangular projection and recess with respect to the side edges of the laminations. It will be evident, therefore, that the core fiux will flow lengthwise, or in the most favorable direction throughout the full length of each lamination, with a fairly uniform distribution of the core flux throughout the cross section of the core as the portion of the joint which is offset from the diagonal and from an adjacent portion'of an adjacent joint between laminations of a contiguous layer runs in the same general direction as the diagonal.

As in the preceding modification, the adjacent layers of, laminations are oppositely arranged as indicated by the dotted lines oi. Fig, 5 in order that the end portions of the laminations of adjacent layers will overlap each other, and since the projections or overlapping portions which extendon either side of the diagonal running between the approximate inner and outer corners of the assembled laminations have approximately the same size or configuration, the laminations may be cut from strip with a minimum of waste and in assembling the laminations these overlapping portions of adjacent ends of laminations of contiguous layers are substantially symmetrical or have about the same amount of overlap on either side of the diagonal. When the core clamps are applied in a manner as described above, the frictional resistance between the over-' lapping portions of the laminations of'consecutive layers of the core will substantially preclude separation of the leg and yoke portions of the core through subsequent use of the device in which the core is incorporated.

In Fig. 6 is illustrated the manner in which the laminations for the core of Fig. 5 may be produced from a long strip 35 of magnetic material which is similar to the strip I5 described above. As in the previous modification, in order that the laminations will fit-properly together with a tight joint between the diagonal ends, the triangular projection from the diagonal should be symmetrical on the opposite sides of a perpendicular erected from the center of the diagonal.

While the invention has been described with particular reference to magnetic cores for transformers and reactors, it is obvious that the inven-.

tion is applicable to magnetic cores generally, including those for motors, generators or other rotating apparatus as well as to other forms of stationary induction apparatus. The methods which have been described above for making a core by cutting the strip generally diagonally crosswise into lengths with projections and interfitting indentations so as to produce no scrap is described and claimed in my copending ap-' plication S. N. 420,425 which is a divisional of the present application, and which issued on October 5, 1943, as Patent 2,330,824.

Having described the principle of my invention in what I consider to represent certain preferred embodiments thereof, I desire to have it understood that the invention is not to be limited to the specific forms described but that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetic core comprising a plurality of layers of straight laminations formed lengthwise from strip material having the most favorable magnetic direction longitudinally of the strip, adjacent laminations of layers having butt joints between ends extending substantially diagonally with respect to the most favorable magnetic direction and extending fromthe vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations, at least one of adjacent butt joints of contiguous layers having a portion offset from the diagonal running from the approximate inner corner to the approximate outer corner of the assembled laminations and. offset from an adjacent portion of said adjacent joint between laminations of said contiguous layer and running in the same general direction as said diagonal so as to provide overlapping between adjacent laminations of contiguous layers at said joints.

2. A rectangular magnetic core structure comprising a plurality of straight laminations punched lengthwise from a strip of magnetic material, the ends of said laminations being mitered along a broken line symmetrical on opposite sides of a perpendicular erected from the center of the diagonal, the adjacent lamination layers being oppositely arranged.

3. A magnetic core comprising a plurality of layers of laminations, said laminations being punched lengthwise from a metal sheet so that the most favorable magnetic direction thereof extends parallel with the direction of the flux path in the laminations, the opposite ends of each lamination being mitered and the laminations being angularly fitted together so that substantially all of the core flux may travel from one lamination to the next substantially without flowing at an angle with respect to the most favorable magnetic direction of the angularly arranged laminations, said opposite ends at the mitered joint having interlocking portions for maintaining the tightness of the joint.

4. A magnetic core comprising a plurality of layers of laminations, said laminations being punched from a metal sheet so that the most favorable magnetic direction of the metal extends in the direction of the flux path in the laminations, the laminations of each layer being fitted closely together at the corners along diagonally cut ends, said diagonally cut ends extending from the vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations so that a minimum of flux passing from one lamination to another will pass crosswise of the most favorable magnetic direction, one end of each lamination having a portion extending outwardly from the diagonal edge and a notch in the opposite end for cooperatively receiving a corresponding projection from the end ofan adjacent lamination, said portions being symmetrical on both sides of a perpendicular erected from the center of the diagonal.

5. A magnetic core comprising a plurality of lamination stacks, the laminations of the stacks being punched from a metal sheet so that the most favorable magnetic direction thereof extends in the direction of the flux path through the laminations, the opposite ends of said lamination stacks having diagonal edges whereby said stacks may be fitted together with mitered corner joints, and means including interfitting portions of the laminations of said stacks for substantially precluding separation of said stacks in the assembled core.

6. A magnetic core comprising a plurality of lamination stacks, the laminations of said stacks being punched from a metal sheet so that the most favorable'magnetlc direction thereof extends in the direction of the core flux path through said laminations, the opposite ends of the laminations of said stacks being cut at an angle whereby said stacks may be assembled with a mitered joint between the laminations of each layer, laminations of one stack having portions projecting from the end thereof for fitting cooperatively into notches provided in corresponding laminations of an adjacent stack, said portions being symmetrical on both sides of a perpendicular erected from the center of the cut ends of the laminations.

7. A magneticcore comprising a plurality of oppositely arranged layers of straight laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations of each layer having a generally diagonally extending butt joint withrespect to the most favorable magnetic direction between ends and extending from the vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations so that a maximum of flux passing from one lamination to another will pass longitudinally of each lamination, said layers being formed of laminations of not more than two different shapes with the laminations of one of said shapes having dissimilar ends, said one of said last-mentioned laminations having dissimilar ends of each layer being oppositely arranged with inspect to a similarly shaped lamination of said layer in order to stagger portions of adjacent butt joints of contiguous layers so that portions of the ends of said laminations of one layer will overlap portions of land-- nations of the contiguous layer.

8. A magnetic core comprising a plurality of layers of assembled laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations of layers having substantially diagonally extending butt joints with respect to the most favorable magnetic direction between ends so that a minimum of flux passing from one lamination to another will pass crosswise of the most favorable magnetic direction, said butt joints being offset from an adjacent diagonal running from the inside corner to the outside corner of the assembled laminations, said adjacent joints between adjacent laminations of contiguous layers being offset on opposite sides of said diagonal so as to provide overlapping between adjacent laminations of contiguous layers at said joints.

9. A magnetic core comprising a plurality of layers of assembled laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations of layers having butt joints between ends extending substantially diagonally with respect to the most favorable magnetic direction and extending from the vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations so that a minimum of flux passing from one lamination to another will pass crosswise of the most favorable magnetic direction, at least one of adjacent of said butt joints of contiguous layers having a portion substantially coincident with an adjacent diagonal running from the approximate inside corner to the approximate outside comer of the assembled bled laminations and running in the same general direction as said diagonal so as to provide overlapping between adjacent laminations of contiguous layers at said joints.

10. A magnetic core comprising a plurality of layers of assembled laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations of layers having butt joints between ends extending substantially diagonally with respect to the most favorable magnetic direction from the vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations so that a minimum of flux passing from one lamination to another will pass crosswise of the most favorable magnetic direction, said butt joints having portions being displaced from an adjacent diagonal running from the inside corners to the outside corners of the assembled laminations at some corners of the assembled laminations, said portions of adjacent joints laminations and at least one of said adjacent of contiguous layers at said corners being substantially symmetrically displaced on opposite sides of the adjacent diagonal,

11. Amagnetic core comprising a plurality of layers of laminations formed lengthwise from strip material having the most favorable mag netic direction lengthwise of the strip, adjacent laminations of layers having substantially diagonally extending butt joints with respect to the most favorable magnetic direction between ends so that a maximum of flux passing from one lamination to another will pass substantially longitudinally of each lamination, and opposite ends of adjacent laminations of said layers providing butt joints with projections and corresponding indentations for cooperatively receiving said projections, said layers being-oppositely arranged so that said projections at ends of laminations of one layer overlap projections of laminations of contiguous layers, said projections of adjacent ends of laminations of contiguous layers being substantially symmetrical on either side of an adjacent diagonal running from the inside corner to the outside corner adjacent said joints oi. the assembled lamination layers.

JOHN C. GRANFIELD. 

